JP2794291B2 - Electrophotographic coated carrier - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a coated carrier for electrophotography, and more particularly to a coated carrier useful for color copying.

[Prior Art] As described in U.S. Pat. No. 2,297,691; Japanese Patent Publication No. 42-23910; Japanese Patent Publication No. 43-24748, etc., electrophotography is performed by corona discharge on a photoconductive layer. To form a latent image by exposing the exposed portion to a light image corresponding to the original, thereby extinguishing the charge in the exposed portion. The development is carried out by adhering a fine powder test substance, so-called toner, on the obtained electrostatic latent image. The toner is attracted to the electrostatic latent image according to the amount of charge on the photoconductive layer, and forms a toner image having a density. This toner image is transferred to a supporting surface such as paper or cloth as needed, and heated,
The toner is permanently fixed to the support surface by using an appropriate fixing means such as pressure, solvent treatment, or overcoating treatment. If it is desired to omit the toner image transfer step, the toner image can be fixed on the photoconductive layer.

In the development of the electrostatic latent image, the toner is mixed with a carrier having relatively large particles and used as a developer for electrophotography. The composition of both the toner and the carrier are chosen such that the toner has a polarity opposite to the charge on the photoconductive layer due to mutual contact friction. As a result of the contact friction between the two, the carrier electrostatically adheres the toner to the surface, transports the developer as a developer in the developing device, and supplies the toner on the photoconductive layer.

There are many known methods for developing a developer. Cascade developing method described in U.S. Pat.
The magnetic brush method described in 874063, the touch-down method described in U.S. Pat. No. 2,895,847, and others, and a bias electric field composed of an AC component and a DC component is applied between a developer carrier (developing sleeve) and a photoconductive layer to perform development. There is a so-called J / B developing method disclosed in JP-A-62-63970.

A typical method is a magnetic brush method. That is, magnetic particles such as steel and ferrite are used as the carrier, and the developer including the toner and the magnetic carrier is held by a magnet, and the developer is arranged in a brush shape by the magnetic field of the magnet. When the magnetic brush contacts the electrostatic latent image surface on the photoconductive layer, only the toner is attracted from the brush to the electrostatic latent image to perform development.

When a large number of continuous copies are made by an electronic copying machine using a two-component developer, a clear image with good image quality can be obtained at the initial stage. The resulting image is poor in tonality and sharpness.

In color copying using chromatic toner, continuous tone is an important factor affecting the image quality. After copying many sheets, the occurrence of an edge effect in which only the peripheral portion of the image is emphasized is caused by the image steepness. The tonality is greatly impaired, and the pseudo reproducibility by the edge effect is formed in the vicinity of the actual contour, thereby deteriorating copy reproducibility including color reproducibility in color copying. Also, in the case of color copying, the image area used is less than 10% of the image area used for conventional black-and-white copying, and the image area is very different from almost line image parts such as letters, documents, reports, etc. At least 20% or more, and solid images with gradations such as photographs, catalogs, maps, and paintings occupy a considerable area.

When continuous copying is performed using such a document having a large image area, a copy having a high image density is usually obtained in the initial stage. Is caused to cause fogging, or the toner density (indicating the mixing ratio of toner and carrier) is partially increased or decreased on the developing sleeve, resulting in image blurring and uniformity of image density. Can not be. This is because the rapid rise of triboelectric charging between the replenishment toner and the carrier in the developer is poor, and it is considered that insufficient development and fogging occur due to the involvement of uncontrolled and insufficiently charged toner in the development. Can be

As a color developer, the ability to always output a high-quality image even in a continuous copy of a document having a large image area is indispensable. Conventionally, in order to cope with an original having a large image area and an extremely large amount of toner consumption, improvement has been made to the developing device rather than to the developer itself. That is, in order to increase the chance of the developing sleeve contacting the electrostatic latent image, the peripheral speed of the developing sleeve is increased, or the size of the developing sleeve is increased.

Although these measures increase the developing capacity, they cause contamination of the inside of the apparatus due to toner scattering from the developing apparatus, and significantly limit the life of the apparatus due to overload on the driving of the developing apparatus.

Further, in order to compensate for the lack of developing ability of the developer, a large amount of the developer may be supplied into the developing device in order to cope with such a problem. As in the case described above, this results in an overload on the driving of the developing device, which is not very preferable.

[Problems to be Solved by the Invention] Until now, it is possible to continuously copy an image having a large image area with a small amount of developer, and it is suitable for a coated carrier in which an edge effect does not easily occur, especially for color copying. At present, no coated carrier has been found.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a coated carrier for electrophotography which does not cause a decrease in image density or a blurring even when a color original having a large image area is continuously copied.

Another object of the present invention is to provide a coated carrier for electrophotography capable of obtaining a color copy having a small edge effect even after durability by repeated copying.

Still another object is to provide a coated carrier for electrophotography in which a rapid rise of triboelectric charging between a toner and a carrier can be obtained.

Yet another object is to provide a coated carrier for electrophotography, which has less environmental dependence of triboelectric charging.

Another object of the present invention is to provide a coated carrier for electrophotography having good transportability in a developing device.

Another object of the present invention is to provide a coated carrier for electrophotography, which has less cracking and chipping of a carrier coating coat in continuous copying of many sheets and has excellent adhesion to a core.

[Means for Solving the Problems] Specifically, the present invention is an electrophotographic coated carrier obtained by coating a core material with a block copolymer, wherein the block copolymer has two or more functions. The present invention relates to a coated carrier for electrophotography, which is a block copolymer produced by a photopolymerization method, in which segments different from each other are connected in a block shape to form a polymer chain.

With the block copolymer used in the present invention, two or more types of segments having different functions are linked in a block shape,
It is a polymer that has formed a polymer chain. In particular, in the present invention, when the two types of segments are, for example, A and B segments, AB, or ABA, BAB, or ABA ...
.. -BAB is preferable.

In this case, the segments A and B share different functions used for carrier coating. For example, one of the segments serves to enhance the adhesion to the core, and also prevents the coating from cracking or chipping due to prolonged collision or mechanical friction. The other segment makes it possible to control the charging characteristics as a coated carrier, the adhesion of moisture that affects the environment dependency, the prevention of spent toner, and the like.

As a material having a function similar to the present invention, there are various coupling agents, and various processing carriers using the same have been proposed. For example, JP-A-58-196550, JP-A-60-221767, JP-A-60-196778, JP-A-61-196778
-7849.

However, the present inventors have found that the use of the block copolymer of the present invention has much higher adhesion to the core material than the use of these coupling agent treatments for coating the carrier core. did. Further, the block copolymer has a variety such that a segment contributing to adhesion and a segment affecting electrophotographic properties can be selected according to the surface properties and material of the carrier core.

The block copolymer of the present invention can be divided into a main segment and a sub-segment which share functions. The ratio of the main segment to the total block copolymer is 51 to 90%, preferably 55 to 80%.

Styrene, acrylic ester,
Methacrylic ester or the like can be used alone or in combination of two or more, for example, polymethyl acrylate,
Polybutyl acrylate, polyethyl acrylate, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-chlorostyrene copolymer, styrene Methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene
Butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-phenyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer And styrene-phenyl methacrylate copolymer and styrene-α-methyl methyl acrylate copolymer.

The sub-segments include (Group A) tetrafluoroethylene, vinylidene fluoride, vinyl fluoride, trifluorochloroethylene, dichlorodifluoroethylene, acrylic acid, methacrylic acid, maleic acid, fumaric acid, and 2-hydroxy methacrylate. A homopolymer or a copolymer comprising at least one monomer selected from the group A of ethyl, 2-hydroxyethyl acrylate, trifluoroethyl acrylate, and trifluoroethyl methacrylate;
Alternatively, a copolymer comprising one or more monomers of Group A and one or more monomers selected from the following Group B may be used.

(Group B) styrene, chlorostyrene, α-methylstyrene, methyl acrylate, ethyl acrylate, butyl acrylate, octyl acrylate, phenyl acrylate,
Methyl methacrylate, ethyl methacrylate, butyl methacrylate, phenyl methacrylate, α-chloroacrylic acid, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate.

In particular, at least one segment of the block copolymer is preferably a fluoropolymer.

The block copolymer of the present invention cannot be achieved by the conventional ionic polymerization method, but can be achieved by using a novel photopolymerization method.

The number average molecular weight of the block copolymer is preferably 5,000 to 30,000, and more preferably 9000 to 20,000.

As the core material of the coated carrier used in the present invention, known materials can be used without departing from the scope of the present invention. For example, iron, nickel, copper, zinc, cobalt, manganese having a surface oxide or unoxidized can be used. , Chromium, rare earth and the like, and alloys or oxides thereof, and ferrite. Preferably, a ferrite selected from zinc, copper, nickel and cobalt metals can be used. In addition, there is no particular limitation on the manufacturing method.

As a method for coating the surface of the core material with the block copolymer of the present invention, the polymer is dissolved or suspended in a solvent, and a method such as a spray dry coating method or a tumbling fluidized bed type coating method is used. Any of the conventionally known methods such as a method of applying and bonding to a core substance by a method described above, or a method of simply mixing with a powder can be applied.

Preferred solvents for dissolving the polymer include methyl ethyl ketone, methyl isobutyl ketone, toluene,
Examples include xylene, monochlorobenzene, dichlorobenzene, and nitrobenzene.

The average particle size of the coated carrier is preferably from 20 to 60 µ, more preferably from 30 to 56 µ. At an average particle size of less than 20μ, the decrease in image density due to charge-up of the toner and an increase in carrier adhesion to the photoreceptor increase.
Fine line reproducibility of color copying will be deteriorated.

The magnetic properties of the carrier of the present invention greatly affect the developing properties and transport of the developer. Especially in color copying, importance is placed on uniformity and gradation of images.

If the saturation magnetization exceeds 300 emu / g (for an applied magnetic field of 3000 Oersted), during development, brush-like spikes composed of carrier and toner on the developing sleeve facing the electrostatic latent image on the photoreceptor will develop. The state becomes tight, and the gradation and the reproduction of halftone are deteriorated. If it is less than 55 emu / g,
There is a disadvantage that the toner and the carrier cannot be easily held on the developing sleeve, and fog and toner scattering are deteriorated. That is, the saturation magnetization is 55 to 300 emu / g, preferably 60 to 300 emu / g.
200 emu / g.

Further, if the residual magnetization and the coercive force of the carrier are too high, the good transportability of the developer in the developing device is hindered, and image defects such as blurring and uneven density in a solid image are liable to occur. It will be close. Therefore, unlike ordinary black-and-white copying, in order to maintain developability in color copying, the residual magnetization and coercive force must be 10 emu / g or less and 1 emu / g or less, respectively.
0 e or less (for an applied magnetic field of 3000 Oe) is preferably 5 emu / g or less, and 6.0 e or less is important.

Regarding the toner used with the coated carrier of the present invention, as the binder resin for the toner, for example, polyethylene,
Chloropolystyrene, poly-α-methylstyrene, styrene-chlorostyrene copolymer, styrene-propylene copolymer, styrene-butadiene copolymer, styrene-
Vinyl chloride copolymer, styrene-vinyl acetate copolymer,
Styrene-maleic acid copolymer, styrene-acrylate copolymer (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-
Butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-phenyl acrylate copolymer, etc., styrene-methacrylate copolymer (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate) Styrene, such as copolymer, styrene-butyl methacrylate copolymer, styrene-phenyl methacrylate copolymer), styrene-α-methyl methyl acrylate copolymer, styrene-acrylonitrile-acrylate copolymer, etc. Resin (a homopolymer or copolymer containing styrene or a substituted styrene), vinyl chloride resin,
Styrene-vinyl acetate copolymer, rosin-modified maleic resin, phenolic resin, epoxy resin, polyester resin, low molecular weight polyethylene, low molecular weight polypropylene,
Ionomer resins, polyurethane resins, silicone resins, ketone resins, ethylene-ethyl acrylate copolymers, xylene resins, polyvinyl butyral resins, and the like can be used.

Preferred resins include styrene-acrylate resins and polyester resins. In particular, (Wherein R is an ethylene or propylene group, x and y are each an integer of 1 or more, and the average value of x + y is 2
~ 10. A) a carboxylic acid component comprising a divalent or higher carboxylic acid or an acid anhydride thereof or a lower alkyl ester thereof, such as fumaric acid, maleic acid, maleic anhydride, and phthalic acid. A polyester resin obtained by at least co-condensation polymerization of an acid, terephthalic acid, trimellitic acid, pyromellitic acid and the like is more preferable since it has sharp melting characteristics.

When the coated carrier of the present invention is mixed with a color toner to prepare a two-component developer, the mixing ratio is 3.0% by weight to 15% by weight, preferably 6% by weight, as the toner concentration in the developer.
Good results are usually obtained at weight percentages of from 13 to 13% by weight.
If the toner concentration is less than 3.0%, the image density is low and it becomes impractical. If the toner concentration is more than 15%, fog and scattering inside the machine are increased, and the useful life of the developer is easily shortened.

As a colorant used when constituting a color developer together with the coated carrier of the present invention, as a dye, for example, CI Direct Red 1, CI Direct Red 4, C.
I. Acid Red 1, CI Basic Red 1, CI Modern Red 30, CI Direct Blue 1, CI Direct Blue 2, CI Acid Blue 9, CI Acid Blue 15,
CI Basic Blue 3, CI Basic Blue 5, CI Modern Blue 7, etc. Pigments include Naphthol Yellow S, Hansa Yellow G, Permanent Yellow NCG,
There are Permanent Orange GTR, Pyrazolone Orange, Benzidine Orange G, Permanent Red 4R, Watching Red Calcium Salt, Brilliant Carmine 3B, Fast Violet B, Methyl Violet Lake, Phthalocyanine Blue, Fast Sky Blue, Indanthrene Blue BC and the like.

Preferably, disazo yellow, insoluble azo, and copper phthalocyanine are suitable as pigments, and basic dyes and oil-soluble dyes are suitable as dyes. Particularly preferred CI Pigment Yellow 17, CI Pigment Yellow 15, CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 12, CI Pigment Red 5, CI Pigment Red 3, CI Pigment Red 2, CI Pigment Red 6, C.
Pigment Red 7, CI Pigment Blue 15, CI Pigment Blue 16, and the like. In addition, CI Solvent Red 49, CI Solvent Red 52, CI Solvent Red
109, CI Basic Red 12, CI Basic Red 1,
CI Basic Red 3b.

As a device for measuring the magnetic properties of the carrier, a BHU-60 type magnetization measurement device (manufactured by Riken Keisoku) is used. The measurement sample is about 1.
Weigh 0 g, pack it in a cell with an inner diameter of 7 mmφ and a height of 10 mm, and set it in the above device.

In the measurement, first, an applied magnetic field is gradually applied to change up to 3000 Oe. Next, the applied magnetic field is reduced, and finally a hysteresis curve of the sample is obtained on the recording paper. Thereby, the saturation magnetization, the remanent magnetization, and the coercive force are obtained.

[Examples] Example 1 To 100 parts by weight of a polyester resin obtained by condensing propoxylated bisphenol and fumaric acid, a coloring agent and a charge control agent having the prescribed amounts shown in Table 1 were used.
Magenta, cyan and black color toners were obtained.

The production method is that the above-mentioned formulation amounts are sufficiently preliminarily mixed with a Henschel mixer, melt-kneaded at least twice with a three-roll mill, cooled, roughly crushed using a hammer mill to about 1-2 mm, and then air-cooled. It was pulverized to a particle size of 40 μm or less by a jet-type pulverizer. Furthermore, the obtained finely pulverized product is classified, 2 to 23 μm is selected so as to have a particle size distribution of the present invention, and a silica fine powder treated with hexamethyldisilazane as a flow improver is added to 100 parts by weight of each classified product. 0.5 parts by weight of an external additive was added to obtain a color toner.

To 8 to 12 parts by weight of the color toner, the coated carrier A shown in Table 2 was mixed so that the total amount became 100 parts by weight to obtain a developer. The developer concentration of each color toner is
9%, 8%, 10%, and 10%.

Copy tests were performed using a color electrophotographic apparatus having the OPC photosensitive drum shown in FIGS. 1 and 2 and a replenishment-development system.

The development and transfer of each color toner were performed in the order of magenta toner, cyan toner, yellow toner, and black toner.

An example of the replenishment-development system used in the present invention will be described. The replenishment toner fed by the supply screw 16 in the toner transport cable 4 is supplied to the toner supply port 15 by the developing device 2.
2 and supplied into the developing device.

When the developing device rotates and comes to a position facing the photosensitive drum 1, the replenishment toner is uniformly mixed with the developer within a very short time by the mixing-conveying screw 12, and the developer having a constant developer concentration is mixed with the developer. Become.

The developer is provided on a developing sleeve 13 with a developer regulating blade.
The amount of the developer becomes a fixed amount due to 14, and the negatively charged toner is transferred onto the photosensitive drum 1 by the reversal development method at the opposite portion of the photosensitive drum 1 having the negatively charged electrostatic latent image.

Using this method, a full-color image faithfully reproducing the original color chart with little edge effect was obtained even after printing for 20 000 sheets using a manuscript having an image area of about 40% in the full-color mode. In addition, an image without blurring and density reduction was obtained even during continuous copying, and the conveyance in the copying machine and the detection of the developer density were good and stable.

Example 2 A magenta toner single color durability test was carried out using the coated carrier B shown in Table 2 by changing the magenta colorant to CI basic red 12,1.0 parts by weight and CI disperse violet 31,0.5 parts by weight. Even after 10,000 copies, a good image density was obtained and a clear image was obtained.

Example 3 Using the coated carrier C shown in Table 2, the cyan colorant was CI
Under a high-temperature, high-humidity environment in the same manner as in Example 1, except that the weight was changed to 6.0 parts by weight of Basic Blue 5, the colorant for yellow was changed to 2.3 parts by weight of CI Disperse Yellow 54, and an original having an image area of 50% was used. (32.5 ° C., 85% RH), a good color-balanced image free of fogging was obtained, and the charging characteristics were stable.

Example 4 Using the coated carrier D in Table 2, the colorant for yellow was C.I.
I. Pigment Yellow 13 was replaced with 6.0 parts by weight, and a yellow single color durability test was conducted in the same manner as in Example 1.
Even during continuous copying, performance was obtained which had no problem in transportability and developer mixing properties.

Comparative Example 1 A test was performed in the same manner as in Example 1 except that the carrier was changed to the coated carrier E shown in Table 2. However, the image density gradually decreased during continuous copying, resulting in poor gradation reproducibility.

This is due to the fact that toner spent on the carrier during the endurance, causing the toner to be scattered in the machine for 50000 sheets due to a decrease in the triboelectric charging ability, contaminating the developer detection fiber and making detection impossible. I made it.

Under high temperature and high humidity, the frictional charge with the toner is remarkably reduced, and the image density of magenta is 2.0 or more according to the Macbeth reflection densitometer, which is extremely high, and the fog on the non-image area is considered to be impractical. Was.

[Brief description of the drawings]

1 and 2 are views showing a color electrophotographic apparatus having an OPC photosensitive drum and a supply-development system.

Claims (2)

(57) [Claims] A coated carrier for electrophotography comprising a core material coated with a block copolymer, wherein the block copolymer comprises two or more types of segments having different functions linked in a block shape. A coated carrier for electrophotography, which is a block copolymer formed by a photopolymerization method and having a molecular chain. 2. The method according to claim 1, wherein the core material is a surface oxidized or unoxidized iron,
2. The coated carrier for electrophotography according to claim 1, wherein the carrier is made of a material selected from the group consisting of nickel, copper, zinc, cobalt, manganese, chromium, rare earth metals and alloys or oxides thereof, and ferrite.